The present invention relates to a device for surgery of the cornea, in particular a keratome capable of slicing a sliver from the cornea, either to separate it completely or to leave it as a flap.
There exist numerous apparatuses suitable for implementing this operation (resection of the cornea). The technique of sliver resection began to be implemented more than 50 years ago and apparatuses have been under development ever since. This development has been directed essentially at two points: the means for cutting the corneal disk and the means for advancing the cornea-cutting means.
Two main types of cutter means are to be found at present: blades with circular motion (such as Prof. Draeger""s microkeratome, for example) and blades with alternating rectilinear motion, including those which lie in the section plane (WO 95/31143) and those, in more widespread use, which slope relative to said plane like the blade of a planing tool (e.g. U.S. Pat. No. 4,462,370).
The blade is driven in the same way, i.e. by means of a motor or turbine whose rotary outlet shaft is connected to the blade either without any modification to its motion, in which case the blade is rotary, or else with the continuous circular motion of the motor being transformed into reciprocating linear motion by a peg secured to the shaft engaging in a groove secured to the blade which then oscillates in a direction perpendicular to the direction of its advance.
The means for moving the cutter blade through the cornea to be resected have in common a ring for fixing a base of the apparatus on the eye, which ring carries guide means that co-operate with a blade-carrier head within which the motion of the blade is sustained. These guide means are of two types, either slideways (generally rectilinear slideways) in which the blade-carrier head is slidably mounted (see document U.S. Pat. No. 4,662,370), or else a pivot about which the blade-carrier head is pivotally mounted (see document U.S. Pat. No. 5,586,980).
The movement of the blade-carrier head along the fixed guide means is driven by the hand of the surgeon. It is limited by an abutment when cutting of the cornea is to be limited to forming a flap that remains connected to the cornea. Proposals have recently been made to motorize this movement by causing rotating means carried by the blade-carrier head to co-operate with fixed means carried by the fixing ring so that the rotating means can roll without sliding along the fixed means (in this context, see the following documents: U.S. Pat. No. Re 35 421, U.S. Pat. Nos. 5,624,456, 5,980,543).
Present devices with motorized advance are devices which the surgeon finds complicated to use. It is not easy to adjust the beginning and the end of the cutting trajectory of the head, and there is no way to act on the travel speed of the blade-carrier head since there is only one motor for driving both the reciprocating motion of the blade and the gearing for advancing the keratome relative to the ring with a speed reduction that locks the frequency of oscillation of the blade and its speed of advance in a ratio that is defined by construction. Finally, those keratomes are not suitable for use by surgeons who prefer to apply manual control over the advance of the keratome across the ring.
The present invention seeks to remedy those drawbacks with a microkeratome that is simple to use and that offers the advantage of satisfying all of the requirements that have been expressed by surgeons.
To this end, the invention thus provides a device for surgery of the cornea, comprising:
an annular base for fixing the apparatus to the eye of a patient;
a cutter head comprising a body and a blade suitable for being displaced along a plane trajectory parallel to the annular base;
guide means for guiding the cutter head relative to the base;
drive means for driving the blade in the cutter head with reciprocating linear motion parallel to its cutting edge; and
drive means for driving the cutter head relative to the annular base along said trajectory.
According to the invention, said drive means comprise two independent motor units surmounting the cutter head and having mutually parallel outlet shafts perpendicular to the plane of the trajectory of the cutter head.
The independence of these drive means provides numerous advantages. It is thus easy with simple electronic means for the operation of each of said means to be servo-controlled to determine fixed or variable parameters and to conditions defining a relationship between them.
Thus, the surgeon can adjust the rate of advance of the cutter head along its trajectory that makes it possible to adjust the rate of advance to the surgeon""s own practices. The controlling electronics can provide for the cutter head to advance at a rate that varies, e.g. as a function of the variation in the surface area of cornea that is in contact with the blade. It is also possible to provide for oscillation to be interrupted during the return stroke of the cutter head.
It is also possible to provide safety features governing the drive which advances the head, specifically stopping the advance if oscillation stops or is faulty, making it impossible to start in the event of a failure of the suction system for holding down the annular base, . . . .
The two drives provided by the invention make it possible for the surgeon to fix the starting point of the trajectory accurately and without possible error so that, at the starting point, the blade is always out of contact with the cornea regardless of the diameter of the corneal cap that it is desired to obtain.
Finally, it should be observed that the independence of the drive means makes it possible to eliminate all of the mechanical gearing, wheel, and wormscrew means that used to be necessary and received in the head for taking transmission from the oscillation shaft for the purpose of advancing the cutter head. Unfortunately, such drive takeoff can only be performed via metal parts since they are the only parts that make it possible to achieve the manufacturing precision required for such small-sized equipment constituting micromechanics. The drive takeoff thus used to provide electrical continuity between the microkeratome motor and the fixing base or ring so the patient was not protected against electrical failure of the equipment during an operation. By eliminating this drive takeoff, the invention makes it possible to use a shaft of dielectric material (plastics material) at the outlet of the motor that drives advance of the head, thereby forming an insulating barrier between the electrical power supply of the motor and the fixing ring (base) in contact with the patient""s eye.